Environmental and occupational pesticide exposure and human sperm parameters: A Navigation Guide review

Global sperm counts have declined in recent decades, coinciding with the proliferation of endocrine-disrupting chemicals, of which pesticides are some of the most common. Previous systematic reviews of epidemiologic studies published between 1991 through 2013 have reported associations between environmental and occupational pesticide exposure and reduced sperm quality, particularly associations with reduced sperm concentration. This systematic review used the Navigation Guide to critically evaluate the current body of evidence examining sperm quality and pesticide exposure in epidemiological studies. PubMed, Scopus, and Web of Science databases were searched for all English-language articles published after September 2012 until August 2021. Original observational studies that assessed human sperm quality parameters, defined as concentration, motility, morphology, and DNA integrity, and individual-level pesticide exposure were included. The risk of bias for each included study and the strength of evidence were evaluated using the Navigation Guide protocol. Nineteen studies assessing environmental or occupational pesticide exposure and sperm parameters were included. Eighteen studies were cross-sectional studies and one prospective cohort; sample sizes ranged from 42 to 2122 men from 14 different countries. Fifteen (79 %) studies found at least one significant association between pesticide exposure and reduced sperm quality. The overall risk of bias across studies was classified as low to moderate. The quality of evidence was determined to be moderate based on systematic evaluation criteria. There were consistent adverse associations between pesticide exposure and sperm motility (63 % of studies) and DNA integrity (80 % of studies). For sperm concentration and morphology, 42 % and 36 % of studies found significant negative associations, respectively. The strength of the body of evidence overall was rated as having sufficient evidence of toxicity. Regarding specific sperm endpoints, there was sufficient evidence that pesticides are toxic for sperm motility and DNA integrity; limited evidence of toxicity for sperm concentration; and inadequate evidence of toxicity for sperm morphology. The studies reviewed here showed consistent associations between pesticide exposure and diminished sperm parameters, particularly sperm motility and sperm DNA integrity. These findings are largely consistent with results of previous reviews, which have found significant negative associations between pesticide exposure and sperm quality in 13 of 20 (65 %) studies published between 1991 and 2008, and in 14 of 17 (82 %) studies published between 2008 and 2012. After thirty years of mounting evidence, actions are needed to reduce pesticide risks to testicular function and male fertility.